The present invention relates to the exhaust cones used in the afterbodies of aeroengines.
In order to reduce noise in the flow ducts around the exhaust cones of aeroengines, it is known to provide a portion of the surface of such a cone with acoustic attenuation panels. Such panels are typically constituted both by a skin or a wall having a multiply-perforated surface that is permeable to the sound waves that are to be attenuated and also by a solid reflecting wall, with boxes or a cellular body, such as a honeycomb, being arranged between those two walls. In well known manner, such panels form Helmholtz type resonators that serve to attenuate the sound waves produced in the duct over a certain frequency range.
The component elements of such a panel are generally made of metal. The partitions of the boxes or of the cellular body are generally connected to the walls by brazing, and they contribute to the structural strength of the part on which they are mounted.
Nevertheless, that type of acoustic attenuation system presents several drawbacks. Firstly it increases the overall weight of the exhaust cone, which is penalizing in the field of aviation where saving weight is a constant concern.
Also, that type of system is relatively difficult to fabricate, in particular when it comes to assembling and centering multiply-perforated metal skins on the axisymmetric structure of the cone.
Furthermore, because of the large coefficients of expansion of metal materials, the multiply-perforated skins need to be mechanically decoupled from the internal carrier structure of the cone, thereby causing the acoustic attenuation system to be more complicated to make.